Search

Scanning superconducting quantum interference device (SQUID) measurements recently revealed enhanced channels of conductivity at the conducting LaAlO/SrTiO (LAO/STO) interface (Kalisky et al. Nat. Mater. 12, 1091 2013). The orientation of the channels and their thermal behavior suggest that they originate as a consequence of the STO tetragonal domain formation which sets in below ∼105 K. In this work, we use polarized light microscopy to acquire images of the tetragonal domains in the same group of LAO/STO samples. We looked at the configuration of the domains (orientation and spacing) and followed their behavior as a function of temperature and back-gate voltage. The optical data agrees with the electrical behavior mapped magnetically. This direct and independent study of the domain structure confirms that the channel-like conductivity in LAO/STO is due to the STO tetragonal domain structure and emphasizes the importance of STO physics to the interfacial properties. These results demonstrate how small structural changes in perovskite crystals strongly influence the electronic characteristics of heterostructures. [ABSTRACT FROM AUTHOR]

Scanning superconducting quantum interference device (SQUID) microscopy is a powerful tool for investigating electronic states at surfaces and interfaces by mapping their magnetic signal. SQUID operation requires cryogenic temperatures, which are typically achieved by immersing the cryostat in liquid helium. Making a transition to cryogen free systems is desirable, but has been challenging, as electric noise and vibrations are increased in such systems. We report on the successful operation of a scanning SQUID microscope in a modified Montana Instruments cryogen-free cooler with a base temperature of 4.3 K. We demonstrate scanning SQUID measurements with flux noise performance comparable to a wet system and correlate the sensor-sample vibrations to the cryocooler operation frequencies. In addition, we demonstrate successful operation in a variety of SQUID operation modes, including mapping static magnetic fields, measurement of local susceptibility, and spatial mapping of current flow distribution.

Electrostatic fields tune the ground state of interfaces between complex oxide materials. Electronic properties, such as conductivity and superconductivity, can be tuned and then used to create and control circuit elements and gate-defined devices. Here we show that naturally occurring twin boundaries, with properties that are different from their surrounding bulk, can tune the LaAlO 3 /SrTiO 3 interface 2DEG at the nanoscale. In particular, SrTiO 3 domain boundaries have the unusual distinction of remaining highly mobile down to low temperatures, and were recently suggested to be polar. Here we apply localized pressure to an individual SrTiO 3 twin boundary and detect a change in LaAlO 3 /SrTiO 3 interface current distribution. Our data directly confirm the existence of polarity at the twin boundaries, and demonstrate that they can serve as effective tunable gates. As the location of SrTiO 3 domain walls can be controlled using external field stimuli, our findings suggest a novel approach to manipulate SrTiO 3 -based devices on the nanoscale.

Local, deterministic manipulation of individual vortices in type 2 superconductors is challenging. The ability to control the position of individual vortices is necessary in order to study how vortices interact with each other, with the lattice, and with other magnetic objects. Here, we present a protocol for vortex manipulation in thin superconducting films by local contact, without applying current or magnetic field. Vortices are imaged using a scanning superconducting quantum interference device (SQUID), and vertical stress is applied to the sample by pushing the tip of a silicon chip into the sample, using a piezoelectric element. Vortices are moved by tapping the sample or sweeping it with the silicon tip. Our method allows for effective manipulation of individual vortices, without damaging the film or affecting its topography. We demonstrate how vortices were relocated to distances of up to 0.8 mm. The vortices remained stable at their new location up to five days. With this method, we can control vortices and move them to form complex configurations. This technique for vortex manipulation could also be implemented in applications such as vortex based logic devices.

Oxide interfaces, including the LaAlO3/SrTiO3 interface, have been a subject of intense interest for over a decade due to their rich physics and potential as low-dimensional nanoelectronic systems. The field has reached the stage where efforts are invested in developing devices. It is critical now to understand the functionalities and limitations of such devices. Recent scanning probe measurements of the LaAlO3/SrTiO3 interface have revealed locally enhanced current flow and accumulation of charge along channels related to SrTiO3 structural domains. These observations raised a key question regarding the role these modulations play in the macroscopic properties of devices. Here we show that the microscopic picture, mapped by scanning superconducting quantum interference device, accounts for a substantial part of the macroscopically measured transport anisotropy. We compared local flux data with transport values, measured simultaneously, over various SrTiO3 domain configurations. We show a clear relation between maps of local current density over specific domain configurations and the measured anisotropy for the same device. The domains divert the direction of current flow, resulting in a direction-dependent resistance. We also show that the modulation can be significant and that in some cases up to 95% of the current is modulated over the channels. The orientation and distribution of the SrTiO3 structural domains change between different cooldowns of the same device or when electric fields are applied, affecting the device behavior. Our results, highlight the importance of substrate physics, and in particular, the role of structural domains, in controlling electronic properties of LaAlO3/SrTiO3 devices. Furthermore, these results point to new research directions, exploiting the STO domains' ability to divert or even carry current., Competing Interests: The authors declare no competing financial interest.

Background: Cecal diverticulitis is frequently indistinguishable from acute appendicitis preoperatively and is sometimes mistaken for carcinoma at laparotomy. The surgeon must be aware of the possibility of diverticulitis of the cecum in the operating room and choose the appropriate treatment., Purpose: Because there is no universal therapeutic approach to these patients, we decided to assess the presenting symptoms, clinical findings, preoperative diagnosis, operative findings determining the proper management of these patients., Methods: A retrospective chart review of 13 patients with pathologically confirmed cecal diverticulitis, who underwent surgery in our department from 1984 to 1998, was undertaken., Results: The mean age of patients was 43.5 years. Right lower quadrant pain and local tenderness were the only clinical findings in 92.3%, with preoperative diagnosis of acute appendicitis in 84.6% of patients. The operative finding in most cases was inflammatory mass of the cecum; in 6 cases it was indistinguishable from perforated cecal carcinoma. Six patients underwent right hemicolectomy, 5 had ileocecectomy, 1 patient was treated by tube cecostomy, and 1 had diverticulectomy. There were three minor postoperative complications: pneumonia, wound infection and lower limb superficial thrombophlebitis., Conclusions: Cecal diverticulitis needs a high index of suspicion for achieving a preoperative diagnosis. We suggest that the operative therapy should be ileocecectomy. The surgical specimen should be examined during surgery and only if carcinoma is found should the patient have a formal colectomy., (Copyright 2000 S. Karger AG, Basel.)

Tangential missile wounds of the head without skull fracture are a known entity. Usually, references in the literature indicate that this type of injury results from a high-velocity missile impact. We present a case of a tangential missile head wound caused by a low-velocity missile. As the range of fire was short, the quantity of energy that might be released could be equated with that released by a high-velocity missile fired from a much longer range. This possibility should be brought to the attention of clinicians as an essential element in this pre-treatment clinical evaluation. We propose a pathomechanical explanation for the development of the clinical state.

The theory that insufficiency of the spermatic cord layers could be the etiological factor in the development of varicocele is reviewed critically. A prospective study of 40 patients operated upon for a left indirect inguinal hernia was done. The spermatic cord layers were excised as a routine part of the operation but combined manual and Doppler examinations revealed no postoperative reflux into the pampiniform plexus. We conclude that the spermatic cord layers probably do not have a major role in the pathogenesis of varicocele.

The gonad-related accessory spleen is a rare anomaly. We report an unusual variant of this condition, featuring two accessory spleens - inguinal and scrotal. This anomaly is important in the differential diagnosis of mass lesions, and the surgical implications are discussed.

A case of localized, perforated diverticulitis of the transverse colon in a 45-year-old woman is presented. Preoperatively, this rare disease is indistinguishable from other acute surgical conditions, and often is mistaken for carcinoma at laparotomy. This report increases awareness of this unusual condition, and emphasizes the clinical, diagnostic, and therapeutic implications. Case reports described in the literature are reviewed.